1. Field of the Invention
This invention relates to a plasma display device, and more particularly to a plasma display panel that is capable of improving the discharge efficiency using a direct current discharge and a radio frequency discharge. Also, the present invention is directed to a method of driving the same.
2. Description of the Related Art
Recently, a plasma display panel(PDP) feasible to the fabrication of large-scale panel has been available for a flat panel display device. The PDP controls a discharge interval of each pixel to display a picture. Such a PDP is classified into a direct current(DC) type and an alternating current(AC) type in accordance with its electrode structure. An electrode is directly exposed to a discharge gas in the case of a DC-type PDP while an electrode is indirectly exposed through a dielectric material in the case of an AC-type PDP.
Referring to FIG. 1, there is shown a discharge cell structure arranged in a matrix pattern in an AC-type PDP with three electrodes. The PDP discharge cell includes an upper plate having a sustaining electrode pair 12A and 12B formed on an upper substrate 10 sequentially, an upper dielectric layer 14 and a protective film 16, and a lower plate having an address electrode 20 formed on a lower substrate 18 sequentially, a lower dielectric layer 22, a barrier rib 24 and a fluorescent layer 26. The upper substrate 10 is spaced from the lower substrate 18 by the barrier rib 24. The sustaining electrode pair 12 consists of a scanning/sustaining electrode and a sustaining electrode. A scanning signal for a panel scanning and a sustaining signal for a discharge sustaining are applied to the scanning/sustaining electrode while a sustaining signal is applied to the sustaining electrode. A charge is accumulated in the upper dielectric layer 14 and the lower dielectric layer 22. The protective film 16 prevents a damage of the upper dielectric layer 14 caused by the sputtering to prolong a life of the PDP as well as to improve an emission efficiency of secondary electrons. Usually, MgO is used as the protective film 16. The address electrode 20 is crossed with the sustaining electrode pair 12. Data signals for selecting cells to be displayed are applied to the address electrode 20. The barrier rib 24 is formed in parallel to the address electrode 20. The barrier rib 24 prevents an ultraviolet ray produced by the discharge from being leaked into the adjacent discharge cells. The fluorescent layer 26 is coated on the surface of the lower dielectric layer 22 and the barrier rib 24 to generate any one of red, green and blue visible lights. An inactive gas for a gas discharge is sealed into the inner discharge space.
After the PDP discharge cell with such a structure was selected between the address electrode 20 and the scanning/sustaining electrode, it sustains the discharge by a surface discharge between the sustaining electrode pair 12. The fluorescent body 26 is luminous by an ultraviolet generated during the sustaining discharge at the PDP discharge cell and hence a visible light is emitted into the exterior of the discharge cell. As a result, the PDP including the discharge cells displays a picture. In this case, the PDP controls a discharge-sustaining interval, that is, a sustaining discharge frequency of the cell to implement a gray scale required for an image display. In this respect, the sustaining discharge frequency becomes an important factor determining the brightness and a discharge efficiency of the PDP. For the sake of such a sustaining discharge, a sustaining pulse having a duty ratio of 1, a frequency of 200 to 300 kHz and a width of about 20 xcexcs are alternately applied to the sustaining electrode pair 12A and 12B. In response to the sustaining pulse, the sustaining discharge generates only one time at an extremely short instant per sustaining pulse. Charge particles generated by the sustaining discharge move a discharge path formed between the sustaining electrode pair 12A and 12B depending on the polarity of the sustaining electrode pair 12A and 12B to thereby form a wall charge on the surface of the upper dielectric layer 14. This wall charge cancels a voltage applied between the sustaining electrode pair 12A and 12B to reduce a discharge voltage loaded in the discharge space, thereby stopping the sustaining discharge. As described above, the sustaining discharge is generated only once at an extremely shorter instant than a width of the sustaining pulse. Most of the remaining time is wasted for a preparation step for the formation of wall charge and the next sustaining discharge. For this reason, since the conventional PDP has a very short real discharge interval compared with the entire discharge interval, it has low brightness and low discharge efficiency. Referring now to FIG. 2, there is shown the structure of a discharge cell arranged in a matrix pattern in a DC-type PDP. The DC-type discharge cell includes a cathode 30 formed on an upper substrate 10, an anode 32 and an auxiliary anode 34 each formed on a lower substrate 18, and a barrier rib 24 formed between the upper substrate 10 and the lower substrate 18 to provide a main discharge space 31 and an auxiliary discharge space 33. The DC-type discharge cell consists of a main discharge cell provided with the main discharge space 31 and an auxiliary discharge cell provided with the auxiliary discharge space 33. Charged particles produced at the auxiliary discharge cell are introduced into the main discharge cell to cause a display discharge at the main discharge cell. The barrier rib 24 is formed in a lattice structure to prevent a mis-discharge between the adjacent cells caused by a diffusive movement of the charge particles generated by the auxiliary discharge. The anode 32 is formed on the lower substrate 18 provided with the main discharge space 31 while the auxiliary anode 34 is formed on the lower substrate 18 provided with the auxiliary discharge space 33. A current limiting resistor 36 is provided between the anode 32 and the lower substrate 18 to limit an overshoot of the discharge current. The DC-type discharge cell having the structure as described above generates the discharge between the cathode 30 and the anode 32 and makes use of an auxiliary discharge in the auxiliary discharge cell so as to lower a discharge voltage in the main discharge cell. In other words, by the auxiliary discharge generated from the cathode 30 and the auxiliary anode 34 in the auxiliary discharge cell, charged particles are produced. Then, the charged particles are moved into the main discharge space 31 through a hole defined between the main discharge space 31 and the auxiliary discharge space 33 and used for a display discharge caused by the cathode 30 and the anode 32.
The DC-type PDP has an advantage in that it has more excellent contrast than the AC-type PDP because a light generated by the auxiliary discharge is shut off by means of a black matrix(not shown) formed on the upper plate. Also, in view of a fact that the AC-type PDP has a time interval at which the discharge is stopped even when a discharge voltage pulse is being applied by a wall charge formed in the dielectric layer while the DC-type PDP generates a continuous discharge when a discharge voltage pulse is being applied, it can be said that the DC-type PDP has a relatively good discharge efficiency. However, the DC-type PDP has a disadvantage in that total discharge efficiency is low due to an energy loss caused by the auxiliary discharge and the resistance.
Further, the AC-type and DC-type PDP rely on only a negative glow discharge having a poor discharge efficiency because the size of the discharge cell is too small, that is, because a distance between the electrodes is very short. In addition, the conventional AC-type and DC-type PDP has a problem in that most of an electric energy applied to the discharge space 21 is wasted to cause a low brightness because a negative glow is used at the time of their luminescence.
Referring to FIG. 3, there is shown the structure of a typical glow discharge tube. It can be seen from FIG. 3 that a negative glow 42A generates in the neighborhood of the cathode 38 while a positive column 42B appears in a shape of tube at the anode 40 when a distance between two electrodes 38 and 40 is sufficiently long. A space between the negative glow 42A and the positive column 42B is called the Faraday dark space. In this case, the positive column 42B is disappeared when a distance between two electrodes 38 and 40 is shortened and the negative glow 42A is reduced when it is more and more shortened. Accordingly, the brightness and the discharge efficiency are lowered. A problem resulting from such low brightness and discharge efficiency becomes serious as a higher resolution is needed, thereby causing more deteriorated brightness and discharge efficiency. Accordingly, there has been attempted a scheme of utilizing a positive column for providing a good discharge efficiency by changing the discharge area or lengthening the discharge path so as to increase the brightness and discharge efficiency within the limited space of the discharge cell. However, to lengthen a distance between the electrodes for the purpose of lengthening the discharge path raises the discharge voltage to cause many difficulties such as a development of a high voltage driving integrated circuit(IC), etc. As a result, it is necessary to provide a novel discharge and driving mechanism that is capable of lengthening the discharge path with the aid of other discharge mechanism in the existent discharge cell structure.
In order to solve such a low brightness and discharge efficiency problem in the PDP, we had filed a patent application regarding to a method of utilizing a radio frequency discharge using a radio frequency of hundreds of MHz as a display discharge. In the case of the radio frequency discharge, electrons do a vibrating motion by a radio frequency signal, so that a display discharge is sustained in a time interval when a radio frequency signal is applied. More specifically, if a radio frequency voltage signal having the polarity alternating continuously is applied to any one of two opposed electrodes, then electrons within the discharge space is moved into one electrode or the other electrode in accordance with the polarity of the voltage signal. When electrons are moved toward any one electrode, if the polarity of the applied radio frequency voltage signal is changed before the electrons arrive at the electrode, then a movement speed of the electrons is gradually decreased and ultimately a movement direction of the electrons is changed, so that the electrons are moved toward the opposite electrode. If the polarity of a radio frequency voltage signal applied to an electrode is changed before electrons within the discharge space arrive at the electrode, then the electrons do an oscillating motion between the two electrodes. Accordingly, when the radio frequency voltage signal is being applied, the ionization, excitation and transition of gas particles are generated continuously without an extinction of electrons. As described above, the display discharge is sustained during most of discharge time, so that the brightness and discharge efficiency of the PDP can be improved. Such a radio frequency discharge has a physical characteristic identical to a positive column in the glow discharge structure. However if both the address discharge and the sustaining discharge are generated by the radio frequency discharge, then a driving of the PDP becomes not only complicated during the addressing, but also a high voltage is required to cause a rise of the power consumption.
Accordingly, it is an object of the present invention to provide a PDP that is capable of improving a discharge efficiency thereof using a radio frequency as well as carrying out a stable addressing.
Further object of the present invention is to provide a PDP driving method that is adaptive for driving said PDP using a radio frequency.
In order to achieve these and other objects of the invention, according to one aspect of the present invention, an address discharge for selecting a display cell is generated by a direct current discharge, and a data written into the selected cell is displayed by a radio frequency discharge. To this end, a PDP according to the present invention a direct current discharging electrode part for applying a direct current to cause a writing discharge within the discharge cells, said electrode part having electrodes crossed with each other; and a radio frequency discharging electrode part for applying a radio frequency voltage to generate a sustaining discharge caused by a radio frequency discharge within the discharge cells.
According to another aspect of the present invention, each of discharge cells in the PDP includes first and second substrates opposed to each other; a cathode formed on the first substrate; a barrier rib formed between the first and second substrates to provide an auxiliary discharge space and a main discharge space; an anode formed on the second substrate provided with the main discharge space; an auxiliary anode formed on the second substrate provided with the auxiliary discharge space; and first and second radio frequency electrodes formed in opposition to the barrier rib providing the main discharge space.
According to still another aspect of the present invention, a method of driving a plasma display panel includes a writing discharge step of responding to an opposite polarity of direct current voltage applied to each of the address electrode and the scanning electrode formed to be opposed to each other to cause a direct current discharge, thereby selecting a display cell; and a sustaining discharge step of sustaining a discharge within the selected display cell with a radio frequency discharge caused by a radio frequency voltage applied to each of first and second radio frequency electrodes.
According to still another aspect of the present invention, a method of driving a plasma display panel includes the steps of initiating a radio frequency discharge at the entire panel; sustaining the radio frequency discharge and generating an erasure discharge selectively in accordance with a gray level of a display cell to stop the radio frequency discharge; and stopping the radio frequency discharge in all the display cells when a sustaining discharge interval is terminated.